1. Field of the Invention
The invention relates to an apparatus for etching a substrate, a method of fabricating a thin-glass substrate, a method of fabricating a TFT (thin film transistor) array substrate, and a method of fabricating a device.
2. Description of the Related Art
A thin film device such as a thin film transistor (TFT) is usually fabricated on an electrically insulating substrate. If a thin film device is to be used for a display device such as a liquid crystal display device, it is usually fabricated on a transparent glass substrate.
In these days, a display device is required to be light, thin and flexible. To this end, a technique for fabricating a thin film device on a resin substrate is developed.
A thin film device can be fabricated on a resin substrate by either a first process in which a thin film device is fabricated directly on a resin substrate at a low temperature to which the resin substrate has a resistance, or a second process including steps of fabricating a thin film device on a glass substrate in a conventional manner, and transferring the thin film device onto a resin substrate.
With respect to the above-mentioned second process, many processes have been suggested as follows.
For instance, there has been suggested a process including steps of fabricating a thin film transistor array on a glass substrate, immersing the glass substrate into hydrofluoric acid solution, supplying vortexes of hydrofluoric acid solution to the glass substrate to thereby etch the glass substrate, and transferring the thin film transistor array onto a resin substrate, in K. Takeuchi, T. Eguchi, H. Kanoh, T, Ito, and S. Otsuki, “High-rate glass etching process for transferring polycrystalline silicon thin-film transistors to flexible substrates”, IEEE Transactions on Semiconductor Manufacturing, Vol. 18, No. 3, 2005, pp. 384-389.
Japanese Patent Application Publication No. 4-116619 (published on April 1992) has suggested a process including steps of adhering a pair of glass substrates to each other on each of which a liquid crystal display device has been already fabricated, and immersing the glass substrates into hydrofluoric acid solution for etching the glass substrates.
Japanese Patent Application Publication No. 2003-323132 has suggested a process including steps of forming a molybdenum film as an etching stopper on a glass substrate, fabricating a thin film transistor array on the glass substrate, and immersing the glass substrates into hydrofluoric acid solution for etching the glass substrates.
The above-mentioned Publications do not describe in detail etching a glass substrate through the use of hydrofluoric acid solution.
However, Japanese Patent Application Publication No. 2003-323132 describes that it takes about 3.5 hours for etching a glass substrate, in which case, an estimated etching rate is about 3 micrometers per a minute.
The above-mentioned IEEE Transactions on Semiconductor Manufacturing describes that if an etching rate is increased by increasing a concentration of hydrofluoric acid in the solution, specifically, if an etching rate is increased to 6 micrometers or more per a minute by doing the same, minute particles insoluble to hydrofluoric acid solution are likely to adhere to a surface of the glass substrate, resulting in that etching uniformity is deteriorated.
In the above-mentioned related art in which a glass substrate is immersed into hydrofluoric acid solution to thereby etch the glass substrate, it was not possible to uniformly etch a glass substrate at a high etching rate. The related art takes more than two hours to etch a glass substrate, causing a problem that a through-put is quite slow as mass-production technique.
Japanese Patent No. 2722798, corresponding to Japanese Patent Application Publication No. 4-116619 published on April 1992, has suggested a method of fabricating a thin liquid crystal display device, including adhering a pair of glass substrates to each other with sealing material being sandwiched therebetween, and etching the glass substrates through lower surfaces thereof to thin the glass substrates.
Japanese Patent Application Publication No. 9-159409 (published on June 1997) has suggested an apparatus for detecting when surface treatment is finished. When an etchant is supplied onto a surface of a substrate for removing a layer formed on the surface of the substrate, the apparatus forms a fluid curtain in an area formed between the surface of the substrate and a measurement plane disposed facing the surface of the substrate. The fluid curtain is composed of the same fluid as the etchant. The apparatus includes an elevator system which contact a measurement window to the surface of the substrate or separates the measurement window from the surface of the substrate, an optical detector for measuring a distance between the measurement window and the surface of the substrate, and a fluid curtain controller which controls the elevator system such that the distance between the measurement window and the surface of the substrate is equal to a standard distance, based on the distance between the measurement window and the surface of the substrate.
Japanese Patent Application Publication No. 10-268247 (published on October 1998) has suggested a method of fabricating a liquid crystal panel, including adhering a first glass substrate and a second glass substrate to each other, introducing liquid crystal into a gap formed between the first and second glass substrates, and etching the first and second glass substrates through surfaces thereof opposite to surfaces thereof through which the first and second glass substrates are adhered to each other.
Japanese Patent Application Publication No. 11-44877 (published on February 1999) has suggested an apparatus for washing a substrate, including a first unit which sprays washing solution to upper and lower surfaces of a glass substrate fed in a single direction, a second unit which sprays pure water to the upper and lower surfaces of a glass substrate for flushing the washing solution, and a third unit for drying the glass substrate. Each of the first and second units is designed to include a plurality of nozzles inclining relative to the direction in which substrates are fed, and a plurality of shower pipes arranged crossing the direction, each having a central portion extending towards the direction, and opposite ends inclining relative to the direction.
Japanese Patent Application Publication No. 2004-363200 (published on December 2004) has suggested a method of etching a substrate, including coating an etchant onto a substrate, and feeding the substrate on a plurality of feeding rollers arranged in parallel with one another. The feeding rollers are kept at the same temperature as a temperature of the etchant.
Japanese Patent Application Publication No. 2005-247687 (published on September 2005) has suggested a method of etching a glass substrate, including immersing a glass substrate into chemical solution, and exchanging the chemical solution to new one before quality of the chemical solution is degraded. The glass substrate is etched at a rate equal to or smaller than 10 micrometers per a minute.
Japanese Patent Application Publication No. 2006-121031 (published on May 2006) has suggested an apparatus for processing a substrate, including a processor which processes a substrate with processing solution, an exhaust pipe through which the processing solution is exhausted out of the processor, a filter arranged in the exhaust pipe, and a ultraviolet ray irradiator which irradiates ultraviolet rays to the processing solution during the processing solution passes through the filter.